Method and apparatus for the production of bent tubes

Abstract

A bent tube is formed by passing a straight tube through a diameter-reducing die such that the central axis of the die forms an acute angle with the direction by which the tube is pulled through the die. The acute angle can be kept constant in order to produce a tube having a constant radius of curvature. Alternatively, the acute angle can be changed during the drawing process to form the tube with a radius of curvature which varies along the tube length.

What is claimed is: 
     
       1. A method of cold drawing a metal tube comprising the steps of: arranging within the die a mandrel having a length which is short relative to the tube length,   spacing the mandrel from the die to define a clearance therebetween which is of smaller diameter than said tube,   cold drawing the tube through the clearance in a direction such that a longitudinal axis of the tube exiting said die forms an acute angle relative to a longitudinal axis defined by said die, and changing said acute angle as said tube is being drawn.   
     
     
       2. A method of cold drawing a metal tube comprising the steps of: arranging within the die a mandrel having a length which is short relative to the tube length, spacing the mandrel from the die to define a clearance therebetween which is of smaller diameter than said tube, and   cold drawing the tube through the clearance in a direction such that a longitudinal axis of the tube exiting said die forms an acute angle relative to a longitudinal axis defined by said die,   said cold drawing step including applying an external force to a rod arranged inside the tube to pull said tube through said clearance, a plurality of guide blocks carried by said rod, said guide blocks sliding along a curved surface disposed adjacent said die, causing said mandrel and die to turn about a pivot during said cold drawing step.   
     
     
       3. A method of cold drawing a metal tube comprising the steps of: arranging within the die a mandrel having a length which is short relative to the tube length, spacing the mandrel from the die to define a clearance therebetween which is of smaller diameter than said tube, and   cold drawing the tube through the clearance in a direction such that a longitudinal axis of the tube exiting said die forms an acute angle relative to a longitudinal axis defined by said die, and turning the drawing die as the tube is being drawn, whereby said angle is gradually decreased.   
     
     
       4. A method of cold drawing a metal tube comprising the steps of: arranging within the die a mandrel having a length which is short relative to the tube length,   spacing the mandrel from the die to define a clearance therebetween which is of smaller diameter than said tube, cold drawing the tube through the clearance in a direction such that a longitudinal axis of the tube exiting said die forms an acute angle relative to a longitudinal axis defined by said die, and   sliding said tube along a curved support surface located at an outlet end of said die.   
     
     
       5. A method according to claim 4, including the step of maintaining said acute angle constant during said cold drawing step. 
     
     
       6. A method according to claim 4, including the step of arranging a mandrel inside the tube blank prior to said cold drawing step, said mandrel being shaped with a cross-section partly decreasingly tapered in the drawing direction, displacing said mandrel a certain axial distance forwards in the drawing direction during the drawing operation. 
     
     
       7. Apparatus for cold drawing metal tubes comprising a drawing die with an approach zone convergent in the drawing direction, said die defining a longitudinal axis, an internal mandrel, the length of said mandrel being short relative to that of the tube, said mandrel having a dimension corresponding to that desired for the final tube, drawing means for drawing the tube through said die in a direction oriented at an acute angle relative to said longitudinal axis of said die so that a longitudinal axis of the tube exiting said die forms an acute angle with said longitudinal axis defined by said die, said die mounted for rotation about a pivot axis, and means for rotating said die about said pivot axis for changing said acute angle during said drawing operation. 
     
     
       8. Apparatus for cold drawing metal tubes comprising a drawing die with an approach zone convergent in the drawing direction, said die defining a longitudinal axis, an internal mandrel, the length of said mandrel being short relative to that of the tube, said mandrel having a dimension corresponding to that desired for the final tube, drawing means for drawing the tube through said die in a direction oriented at an acute angle relative to said longitudinal axis of said die so that a longitudinal axis of the tube exiting said die forms an acute angle with said longitudinal axis defined by said die, said drawing means comprising a rod having a tube attachment end for pulling the tube, guide means carried by said rod, and means defining a guide surface at a tube outlet end of said die along which said guide means travels, said guide surface oriented at an acute angle relative to said longitudinal axis of said die for guiding said rod in said direction. 
     
     
       9. Apparatus according to claim 8, wherein said guide surface is curved.